The present invention relates generally to an optimal engine control system, and in particular to an intake air density compensation system for optimally controlling a diesel engine by compensating the control amount of the diesel engine in accordance with the variations of intake air density of the diesel engine.
Generally, a diesel engine of a motor vehicle is designed so that the ignition condition of fuel to be supplied thereto is optimized when the motor vehicle is driven at a flatland. Therefore, when driven at a high altitude, it will be required to compensate for the injection fuel amount in connection with a decrease in intake air density in order to prevent the diesel engine from making worse the emission and drivability.
In a prior art technique, various sensors such as an atomospheric pressure sensor and an intake air temperature sensor have been provided in the diesel engine in order to obtain intake air density information. However, this provision results in an increase in the number of parts and production cost, and further difficulty in maintenance and inspection.
One possible solution is to derive the intake air density information as a function of engine operating parameters obtained by various engine operating condition sensors already attached to the diesel engine.
On the other hand, Japanese Patent Provisional Publication No. 58-47130 discloses a feedback control system wherein a fuel injection timing or ignition timing is controlled in accordance with the variations of the pressure in the inside of the cylinder sensed by a pressure sensor attached to a glow plug, or the operation of the fuel injection nozzle detected by an electromagnetic pickup associated with a nozzle valve.
As a result of an examination in terms of ignition timing control paramenters obtained by a technique disclosed in the above-described prior art, it has been found that one or more ignition timing control parameters represent the intake air density information.